read-char

ToC

Allegro CL

ANSI Common Lisp

21 Streams

21.2 Dictionary of Streams

21.2.17 read-char

Function

Syntax:

read-char &optional input-stream eof-error-p eof-value recursive-p

char

Arguments and Values:

input-stream - an input stream designator. The default is standard input.

eof-error-p - a generalized boolean. The default is true.

eof-value - an object. The default is nil.

recursive-p - a generalized boolean. The default is false.

char - a character or the eof-value.

Description:

read-char returns the next character from input-stream.

When input-stream is an echo stream, the character is echoed on input-stream the first time the character is seen. Characters that are not echoed by read-char are those that were put there by unread-char and hence are assumed to have been echoed already by a previous call to read-char.

If recursive-p is true, this call is expected to be embedded in a higher-level call to read or a similar function used by the Lisp reader.

If an end of file₂ occurs and eof-error-p is false, eof-value is returned.

Examples:

 (with-input-from-string (is "0123")
    (do ((c (read-char is) (read-char is nil 'the-end)))
        ((not (characterp c)))
     (format t "~S " c)))
#\0 #\1 #\2 #\3
  NIL

Affected By:

*standard-input*, *terminal-io*.

Exceptional Situations:

If an end of file₂ occurs before a character can be read, and eof-error-p is true, an error of type end-of-file is signaled.

See Also:

read-byte, read-sequence, write-char, read

Notes:

The corresponding output function is write-char.

Allegro CL Implementation Details:

None.